Exaust stains on Lancasters.

[Stuck]

Hi, Im just getting to the painting stage where i am debating whether to paint exhaust stains on the Lancaster that i am building; However in the past I have spoilt a few models trying to do this ; After looking at a good few pics I notice that there doesnt seem to be any on the outboard exhaust on the Lancaster, can any of you give me a reason for this ? ; i would be very grateful if any of you could give me any hints and tips on how to achieve this effect successfully ; Thanks.

[rs2man]

The outboard engine nacelle hangs vertically off a dihedralled wing , so the inboard exhust goes over the wing , but the outer exhaust goes mainly under the wing

[lufbramatt]

The outer exhaust stains go under the wing due to the dihedral on the outer wing sections ;-) The other ones get sucked over the top.

Lots of people make the mistake of using black for exhaust stains, use shades of oily brown all the way to an almost cream colour in the middle (think the light staining was caused by the pilots leaning the mixture right out to save fuel, raising the exhaust gas temperature). Go easy and stop before it looks overdone. Less = more

[ben_m]

See:

http://www.britmodeller.com/forums/index.php?/topic/64466-a-quick-question-about-exhaust-streaks/

and

http://www.britmodeller.com/forums/index.php?/topic/10212-lancaster-the-exhaust-theory/

[thx6667]

Google around and you'll find some pics, this one illustrates nicely the way the staining flows across the wing, save for the very outboard exhausts. Its a mix of greys and browns.

http://www.flickr.com/photos/ww2images/6897745127/sizes/z/in/photostream/

[Test Graham]

You'd get black/dark exhaust smoke/stains if the engine was running rich, as perhaps on takeoff or under sudden changes of power, when incomplete combustion leads to carbon particles escaping into the exhausts. When the engine is ideally set for maximum range you'd be getting full combustion so the exhaust stains would be grey from the lead additive. Under normal Bomber Command operations you'd expect to see a mix. Battle of Britain Spitfires would tend to have dark exhaust stains, RAAF Mk.VIIIs would tend to have grey ones. Not all pilots were fully informed as to the best way to get maximum range: it is claimed that Lindberg usefully extended the range of P-38s in the Pacific, but from what was said he was basically teaching proper practice. Perhaps the pilots were a little more prepared to listen to another pilot with great credibility.

[Work In Progress]

I was just about to make much the same point as Graham, but he made it better, while I was still typing.

Curiously, the tradition of inexperienced pilots resisting the correct use of the mixture control on piston engined types, often because of what they were taught as a short-cut in early flying lessons, continues to this day.

Edited February 8, 2013 by Work In Progress

[Daniel Cox]

Hi All,

One other point worth mentioning is that the exhaust staining will often start as a dark brown and then given a little time turn grey.

All images Copyright ©2012-2013 Daniel Cox.

Cheers,

Daniel.

[elger]

I'm wondering to what extent exhaust staining on warbirds is similar to that of war era aircraft: is the type of fuel different and does that influence staining? Lead content, that sort of thing?

[Caerbannog]

Judging from my motorcycles and cars manyfolds it is more a matter of how worn an engine is and or how rich/poor the mixture is, probably also a matter of RPM (hotter gases I suppose). My Yamaha has light cream colour at the start of the manifold and my Morris a much darker colour. The Morris has a replacement engine for 10 years now and the colour was a sooty black before - with leaded and later with unleaded fuel (no colour change inside the manifold). With the replacement engine the colour inside the maifold got lighter and I would say it has become a bit darker by now (I used the Morris on a daily basis untill about 6 years ago). But this is somehow in contrast to Daniels pictures, where the stains get lighter. I would say the stains get darker when there is more oil burned (worn out engine) or when the mixture is very rich. Maybe a rich mixture is/was used to run in new or overhauled engines and after running in a leaner mixture was used?

Another thing I can imagine is that the exhaust staining on aircraft which fly mainly "short trips" will have darker stains - again just based on what I see in my garage... So maybe Fighters which mainly protected their airport will have darker stains than figher on long escort sorties if you know what I mean.

I also have the feeling that the exhaust strains look light on dark coloured aircraft and dark on light coloured aircraft. Has anybody an idea about that? Is it just a matter of contrast (so you do not see dark stains on dark aircrafts on b&w pictures)?

[richdlc]

like others have said - inboard six exhausts = over wing. Outboard two = not over wing.

to achieve the effect it's best to airbrush it. Failing that, use pastels.

[Work In Progress]

I'm wondering to what extent exhaust staining on warbirds is similar to that of war era aircraft: is the type of fuel different and does that influence staining? Lead content, that sort of thing?

See Graham's post, really, for the type of usage. If you see a P-51D that spends most of its time ground-running, taxiing and doing 20 minute display flights, it is spending a much greater proportion of its running time in rich mixture than one that's just returned from a six hour escort mission to Berlin and back. But transport and trainer types, Tiger Moths, Harvards, C-47s and so on, are broadly used in the same way now as they were in WW2.

As for the fuel, all other things being equal the higher the tetraethyl lead (TEL) content, the greater the light grey staining. Also of course people devote much more time to keeping their valuable and historic aeroplanes clean and tidy.

Nowadays the usual fuel is AVGAS 100LL. The "LL" stands for "low lead", but that's only "low" in comparison to the higher octane fuels developed during WW2. It is still pretty toxic stuff compared to the old 4-star leaded car petrol. It contains about 0.3–0.5 grams of per litre, more than twice as much as 4-star when that was phased out at the end of the 1980s.

AVGAS 100/130, probably the mainstream WW2 allied aviation fuel, contained about twice as much TEL as 100LL, and AVGAS 115/45, the fuel of choice for high powered late-war piston engined warplanes, and the post-war piston-engined airliner era, had more still. However, those fuels are practically extinct.

Edited February 8, 2013 by Work In Progress

[elger]

See Graham's post, really, for the type of usage. If you see a P-51D that spends most of its time ground-running, taxiing and doing 20 minute display flights, it is spending a much greater proportion of its running time in rich mixture than one that's just returned from a six hour escort mission to Berlin and back. But transport and trainer types, Tiger Moths, Harvards, C-47s and so on, are broadly used in the same way now as they were in WW2.

As for the fuel, all other things being equal the higher the tetraethyl lead (TEL) content, the greater the light grey staining. Also of course people devote much more time to keeping their valuable and historic aeroplanes clean and tidy.

Nowadays the usual fuel is AVGAS 100LL. The "LL" stands for "low lead", but that's only "low" in comparison to the higher octane fuels developed during WW2. It is still pretty toxic stuff compared to the old 4-star leaded car petrol. It contains about 0.3–0.5 grams of per litre, more than twice as much as 4-star when that was phased out at the end of the 1980s.

AVGAS 100/130, probably the mainstream WW2 allied aviation fuel, contained about twice as much TEL as 100LL, and AVGAS 115/45, the fuel of choice for high powered late-war piston engined warplanes, and the post-war piston-engined airliner era, had more still. However, those fuels are practically extinct.

thank you for that detailed response. what I'm also wondering about is the average service life of frontline ww2 aircraft. I think I read somewhere a few years ago that they were only used for about 2-3 months, which is only a fraction of the total lifespan of a warbird. I'm wondering if that also influences to what extent we can look at warbirds and use them as reference for staining and weathering around engines. although warbirds probably better maintained in the short term - being pampered like the priceless artifacts that they are - the long term weathering effects (i.e. metal changing colour due to heat etc) might be different.

[Dave Fleming]

like others have said - inboard six exhausts = over wing. Outboard two = not over wing.

to achieve the effect it's best to airbrush it. Failing that, use pastels.

I would say 'outer two - much less pronounced' - if you look at wartime photos, you sometimes see a dark staining over the outer wing, rather than the grey/brown of the inner ones. And they are not always the same!

[Stonar]

The starboard outer engine in that Life photograph clearly had a problem. I would suggest that the darker stain was caused by oil,look at the tailplane on that side.

I do mine a bit subtler than that piccy

Steve

Edited February 9, 2013 by Stonar

[Miggers]

thank you for that detailed response. what I'm also wondering about is the average service life of frontline ww2 aircraft. I think I read somewhere a few years ago that they were only used for about 2-3 months, which is only a fraction of the total lifespan of a warbird. I'm wondering if that also influences to what extent we can look at warbirds and use them as reference for staining and weathering around engines. although warbirds probably better maintained in the short term - being pampered like the priceless artifacts that they are - the long term weathering effects (i.e. metal changing colour due to heat etc) might be different.

Wartime Merlins were "lifed" at 25 combat hours,i.e they weren't expected to last more than 25 hours before

being shot down or damaged beyond use,not 25 until mechanical failure and as such,were never the most

"oil-tight" things in the world.

That's the main reason for the underside of wartime Merlin powered fighters being very oil streaked.

As we now know,Merlins are very capable of running for more than 25 hours.

Back to the OP's question though,what you've been told in the other post is basically correct.

The Lanc's outer engine's outer pipes pretty much exhausted under the wing.

Staining was usually a light brownish/grey due to Flight Engineers leaning out the mixture

as much as they dared.

Around 1 Air-Mile-Per-Gallon was accepted as a good figure on fuel consumption,plus

weather at a home airfield was never predicted as well as today nor was it accepted that it

would be good,so it was handy to have plenty of fuel left for diversions or orbiting one's

home airfield due to delays in landing "slots"

[Work In Progress]

Discolouration of metal through exhaust heat happens within a few hours of use at operating temperatures. In terms of exhaust stains, a couple of long missions on high-lead fuel are more than enough to build up a pattern.

thank you for that detailed response. what I'm also wondering about is the average service life of frontline ww2 aircraft. I think I read somewhere a few years ago that they were only used for about 2-3 months, which is only a fraction of the total lifespan of a warbird. I'm wondering if that also influences to what extent we can look at warbirds and use them as reference for staining and weathering around engines. although warbirds probably better maintained in the short term - being pampered like the priceless artifacts that they are - the long term weathering effects (i.e. metal changing colour due to heat etc) might be different.

[Stuck]

Well thanks for all your replies, seems to have opened a whole can of worms !! . It seems obvious after what i have read here is that they would have been filthy after a few runs out, and that the lovely yellow tail fins on my model would have been nearly black! . Preferring to finish my models in a more pristine condition i will take the bull by the horns and give it a go, assuming that mine had just been delivered to the airbase by one of those lady pilots who was very careful on the controls, and the ground crew lovingly washed and polished it !! ;

But then again thinking about it, that decal i put on last night showing how many bombs that it had dropped would give that game away !! ;

[Edgar]

This is taken from the Merlin II manual, but probably held good for all Marks of Merlin:-

Engine inspections were normally at 10-hour intervals, with the work involved gradually increasing (e.g. the plugs were to be reconditioned at 20 hours) until a full rebuild would be called for at about 100-120 flight hours. Thousands of Merlin engines were rebuilt and refurbished during the war.

Full throttle was normally 3000 rpm, with maximum continuous cruise at c90%, or 2650 rpm, with boost being used, as well as the throttles, to control speed; also popular Flight Engineers were those who were adept at synchronising the engines' notes, thereby easing the strain on ears.

The uninformed make much of the typical bombing height, for the Lancaster, as being about 18,000', commenting on how the engines must have been straining, and therefore overworked; this is a fallacy, since it was the prevailing meteorological conditions that dictated the height. At around 20,000', and above, is the point at which contrails start, and (especially in moonlight) the last thing a pilot needed was four white fingers pointing out, to fighters and guns alike, "Here I am." It's possibly why the Lancaster didn't make much (any?) use of the 60-series Merlin, which was best above 20,000', freeing it for the Spitfires.

Edgar